Fluorescent lamps of all types are now used in lieu of incandescent bulbs for several reasons. To begin with, the energy requirement to operate a fluorescent lamp is much less than the energy requirement to operate an incandescent or halogen lamp having the same lumen output. Additionally, the quality of the light output from fluorescent lamps has newly improved color spectral output, making their light more pleasing that it had been in the past. Moreover, fluorescent lamps are available in a wide variety of shapes and sizes and thus are better meeting size requirements. Examples of different types are linear fluorescent lamps, compact fluorescent lamps and circline (circular) fluorescent lamps. However, in the case of the use of compact fluorescent lamps, especially for 18 watt and higher powers, the required ballast's cost often deters lighting users from choosing compact fluorescent lighting instead of incandescent lighting, even though in the long run, their energy costs savings would more than make up the difference.
Ballasts are a necessary component of fluorescent lighting because fluorescent lamps require current limiting and a starting voltage higher than the typical household or industrial line voltage. Thus, a fluorescent lamp fixture always includes a ballast such as an iron core inductor or one consisting of electronic components. When connected between the power source and the lamp, a ballast provides limited current and a proper starting voltage. Each type and size of fluorescent lamp has a particular current requirement and therefore to accommodate the wide number of variations, different types of ballasts are manufactured. However, since certain linear fluorescent lamps are used much more pervasively than compact fluorescent lamps, ballasts for these linear fluorescent lamps are the most inexpensive type available.
Recently, particular types of lamp fixtures have been designed for halogen lighting, which is particularly bright. However, halogen lamps in certain fixtures have recently been shown to present a fire danger and therefore their use is discouraged or in some cases, restricted. In such fixtures, a single compact or circline fluorescent lamp might not meet the user's lumen output requirements, but two such compact or circline fluorescent lamps will. The problem remains to provide a ballasting method which fits halogen lamp fixtures to operate compact or circline fluorescent lamps and which is inexpensive enough to appeal to most consumers.
Typically, common (very inexpensive) T8 or T12 ballasts are used to operate two T8 or T12 four-foot linear fluorescent lamps. On the other hand, a compact fluorescent lamp of choice, such as an F36 lamp, requires the use of a ballast which is not produced in mass quantities and is therefore quite expensive. In this manner, the cost of ballasts for compact fluorescent lamps oftentimes inhibits their use by manufacturers for the mass consumer market.
While widely available, these inexpensive T8 or T12 two-lamp ballasts will not generally operate a single compact fluorescent bulb at the proper current, nor are they dimmable. Previously, there has been no utilization of a T8 or T12 ballast with a single F36 compact fluorescent lamp since that lamp does not have the same arc voltage and current ratings as two four-foot linear lamps for which common electronic ballasts were designed. However, it would be extremely desirable to be able to use a common T8 or T12 ballast (or comparable ballast) with a single F36 lamp (or comparable compact fluorescent lamp). Moreover, it would be also desirable to use a common T12 ballast with a plurality of F36 lamps with a multi-way switching capability, which in essence provides dimmability. That is, three-way switchability would include 0%, 50% and 100% illumination. A four-way switchability would include 1/3 illumination, 2/3 illumination and full light levels, as well as "off."
The most common inexpensive ballast type is the series-sequence, rapid-start, two-lamp type. This is true for both the magnetic and electronic types. There are two types of lamps, the four foot T8 (32 watt) and the four foot T12 (40 watt). Each of these require different ballasts. The T8 lamps have a reference current of 265 mA, while the T12 lamps have a reference current of 430 mA. The T8 lamps require a higher starting voltage and have a higher operating voltage as well.
Another very common type, especially with the widespread use of electronic ballasts with T8 lamps, is the parallel, instant-start, electronic ballast. This ballast type is commonly available in two, three, and four-lamp types.
Electronic ballasts have two common types of lamp drive circuitry, the commonly-called "voltage-fed series resonant" (VFSR) type and the commonly-called "current-fed parallel resonant" (CFCR) type. The VFSR circuitry is often employed with rapid-start ballasts and the CFCR is often employed with instant-start ballasts, although the reverse combinations are also found.
In general, compact and circline lamps do not have an operating current and/or voltage that matches well with the above discussed common inexpensive ballast types. Often, the common ballasts will provide too much current for higher power compact or circline lamps, especially if a two-lamp ballast is used to operate a single lamp. Even if the current is close enough, the voltage across the output of a rapid-start VFSR type may be too low to allow proper operating filament voltage.
Previously, multi-way switching and/or dimmability has been achieved by different methods. For example, U.S. Pat. Nos. 4,414,489 and 5,424,610, describes two separate one-lamp ballasts with switching of AC power to none, one or both. While the switch is simple, the two separate ballasts are extremely expensive, occupy too much space, and have half the reliability of a two-lamp ballast. Moreover, two-lamp dimming ballasts as described in U.S. Pat. Nos. 5,315,214; 5,099,176; 5,457,360; and 5,245,253 are available but are relatively expensive.
An inexpensive ballast configuration for switchably and, therefore, dimmably illuminating one or more higher power compact fluorescent lamps is desirable for the replacement of incandescent or halogen lamps. Moreover, were a compact or circline fluorescent configuration to easily fit in a lamp fixture designed for halogen lamps, specifically a fixture known as a torchiere, there would be a beneficial reduced need for the use of halogen lamps. Moreover, it would be beneficial to provide a multi-switching capability which itself, is simple, inexpensive and dissipates substantially no heat.